1. Field of the Invention
This invention relates to an ozonizer of the type provided with a pair of electrodes one of which has a surface facing the other electrode covered with a dielectric, which electrodes are connected to an energy supply source and a parallel connected storage capacitor.
2. Description of the Prior Art
Ozonizers are being used in increasing numbers in industrial applications, because ozone is being used as a strong oxidation medium for waste water purification, air quality improvement, drinking water treatment, food storage, as well as in medicine and chemistry.
A method and a device for carrying out corona discharge reactions is known from the German OS 26 17 104 in which a reaction gas is passed through a corona discharging slot and electrical energy in the form of a narrow impulse is generated in the slot. The formation of a corona discharge transfers energy to the electrons and gas ions found in the slot. The electrons are charged with energy in order to produce a productive reaction with the reaction gas. The gas ions created during the reaction are removed from the slot to minimize any unproductive energy deposition to the ions. The elimination of the gas ions is carried out by pre-tension voltage and in the time interval between the narrow impulses. The gas ions can also be neutralized by the admixture of negatively charged, finely distributed liquid and solid particles. A method of ozone production is used, whereby ozone is produced from a gas mixture containing oxygen which contains considerable amounts of moisture and other impurities.
With such a method the impulses are produced by a relatively expensive switch circuit having a switching element which must be able to switch the entire current. The switching elements used to control such pulsating ozonizers must be able to switch voltages of 15 to 20 kV as well as currents from 1 to 5 kA before a discharge has built up between the ozonizer electrodes. In addition, these switching elements must provide a long service life, i.e., up to 10.sup.10 switching cycles are required. Suitable switching elements are, for example, semi-conductor switches such as break-over diodes and amplifying gate thyristors. Their construction and method of operation are described, for example, in the BBC publication D HS 704 68 EFD and in the publication by P. F. Pittman, D. J. Page, Solid State Pulse Switching, Pulsed Power Cont., Lubbock (Tex), 1977. These switching elements are able to handle the required current increases at a magnitude of 10.sup.9 A/S. Their electric strength, which is at 1 kV, is not sufficient, however. Therefore, switches were suggested and patents applied for with which the switching element needs only a small current increase which is imposed over a slower fundamental oscillation. (See U.S. application Ser. No. 174,259 filed July 31, 1980).
Another disadvantage is the limited current-carrying capacity of the break-over diodes, which can switch at an optimum current of 100 to 200 A per element. It is advantageous to have relatively high current densities on the ozonizer electrodes, c. 1 A per cm.sup.2 of electrode surface to improve the yield of ozone. This is due to the fact that a homogeneous discharge is not produced until these conditions are achieved. An ozone tube, 1 m in length has an electrode surface of approximately 1600 cm.sup.2. Eight to 16 parallel break-over diodes are necessary. Each switches 100 to 200 A to the electrodes in order to produce the necessary current density on the electrodes with such an ozonizer. The ignition current of the individual parallel break-over diodes varies, however, from element to element. Therefore, additional switching measures are needed to assure synchronized switching of the trip diodes and a uniform distribution of the current to the switching elements. Without these additional switching measures a portion of the trip diodes would be overloaded and destroyed.